1. Field of the Invention
This invention relates to a base isolation device for a structure, and more particularly to a base isolation device for a structure that is applied to a structure having structural members such as slabs in elevated freeways, elevated railway tracks, or bridge constructions, and suppresses vibration in the out-of-plane direction of the structural members.
Moreover, the invention can also be applied to a base isolation device that suppresses vibration in the out-of-plane direction of structural members of an inclined roof, or structural-support members of a vertically placed glass curtain wall.
2. Description of the Related Art
In recent years, various measures have been employed for suppressing damage such as collapse or failure of structures comprising structural elements such as the slabs in elevated freeways, elevated railway tracks, or bridge constructions due to vertical vibration of the structural members that occurs during traffic vibration or an earthquake, and one of the measures that has been proposed is the base isolation device shown in FIG. 5.
The base isolation device that is indicated by reference number 1 in this FIG. 5, is applied to a floor slab 3 that is arranged horizontally as a structural member that is supported by a plurality of bridge supports 2, for example, and underneath the floor slab 3, in about the center between the bridge supports 2, an elastic member 4 comprising a spring or the like, and a damping member 5 comprising an oil damper or the like are suspended such that they are parallel with each other, and a weight member 6 is attached to the bottom section of the elastic member 4 and damping member 5.
In this prior base isolation device 1 constructed in this way, when vibration in the out-of-plane direction (in the vertical direction in the example shown in the FIG. 5) occurs in the floor slab 3, the vertical vibration of the floor slab 3 is suppressed by damping the relative motion between the floor slab 3 and the weight member 6 by the elastic member 4 and damping member 5.
In this kind of prior art, there still remain the following problems that must be improved.
In other words, in the prior art described above, in order to efficiently suppress the vertical vibration in the floor slab 3, it is necessary to properly set the elastic coefficient of the elastic member 4 and the damping coefficient of the damping member 5 in accordance to the characteristic natural frequency of the floor slab 3, however, in order to do this, there is a problem in that the range capable of obtaining an effective base isolation function is narrow, and the setting of which is difficult.
Moreover, the weight member 6 is more effective the heavier it is, however, in an actual structure, it was difficult to attach a weight that was 10% the weight of the entire structure.
Furthermore, since the weight member 6 acts only in the direction of gravitational acceleration, installing this prior base isolation device in the structural members of an inclined roof, or the structural-support members of a vertically placed glass curtain wall was impossible.